MicroRNAs derive from the long strain RNA prime transcription products (pri-miRNA) with a length of about 1000 bp; the pri-miRNA molecules are cut in the nucleus by Drosha enzymes into miRNA precursors with a stem-loop structure and a length of about 60-80 nt. As the double-strand miRNA unfolds, the mature miRNA enters the RNA-induced silencing complex (RISC) and pairs completely or incompletely with the complementary mRNA, so as to degrade the target mRNA or prevent the expression thereof. The pri-miRNAs are transported into the cytoplasm and further cut into double-strand miRNAs with a length of 18-26 nt. As the double-strand miRNA unfolds, the mature miRNA enters the RNA-induced silencing complex (RISC) and pairs completely or incompletely with the complementary mRNA, so as to degrade the target mRNA or prevent the expression thereof.
Although microRNAs take only a small share of the cell total RNA, they take part in a series of important life processes, including early-stage embryo development, cell reproduction and cell death, cell apoptosis and fat metabolism, cell differentiation and gene expression regulation. It is common to observe in tumors irregularities of cell reproduction and apoptosis, therefore the irregular absence, mutation or over-expression of miRNAs are conjectured as being able to cause human diseases.
In the long history of evolution, the mammals have acquired a complicated system of self-evaluation and balancing in immune regulation, so as to ensure that the body can maintain a state of self-tolerance while offending the external antigens, of which many mechanisms are however until now not yet completely disclosed.
Recently it is proved with more and more evidences that miRNAs play an extremely important role in immune regulation and the development of immune cells, but only a relatively small number of specific miRNAs are disclosed as important regulators of the immune system. People know still little about the functions of miRNAs, especially in the tumor immune related field.
Therefore, it is an urgent need in the field of tumor treatment to learn about the functions of various miRNAs, so as to discover new medicines for tumor treatment.